Edwin h



Patented Get. 30, 1923.

UNITED STA-TES PATIENT OFFICE.

EDWIN H. COLPTTS, OF EAST ORANGE, NEW JERSEY, .ASSIGNOR TO WESTERNELEC- TRIO COMPANY, INCORPORATED, rOF NEW.YORK, N. Y., A. CORPORATION OF NEW YORK.

Application mea July e,

To all whom. 'it may concern:

Be it known that I, EDWIN H. Conrrrfrs, a subject of the King of Great Britain, re siding at East Orange, in the countyof EsseX, State of New Jersey, have invented certain new and useful Improvements in Multiplex Signaling Systems, of which the following is a full, clear, concise, and exact'description.

rlhis invention relates to signalingY systems employing currents of high frequencies on wires, and particularly has to do with repeating means for repeating signals between a high-frequency multiplex line and lowfrequency circuits.

A feature of the invention lies in the provision of means for selecting thev desired higlrfrequency current from the multiplex line and transmitting high-frequency current to said line, in an efficient manner.

@ther features are concerned in the generation and modulation of the high-frequency currents according to signals on the low frequency lines, and the detection of the high-frequency currents in accordance with their modulations for producing signals on the low-frequency lines.

In the system of multiplex signaling, lrnown as the carrier-wave system, currents of definite frequencies considerably above the signal frequencies are employed, each modulated in accordance with the desired signals. The modulated wave is therefore not a simple wave of a single frequency, but may be thought of as having frequencies varying between comparatively narrow limits either side of the carrier frequency itself. In providing a selective path for the transmission of modulated waves, it is necessary for eiiicient transmission to make the path conductive not simply to the carrier or base fre quency alone, but substantially equally oonductive to the range ofy frequencies embraced in the modulated wave. In radio telephony it is known that a simple series-resonant circuit has been used to transmit selectively a voice-modulated wave of radio frequency. But such a tuned circuit has been found insufficient for voice-modulated carrier waves of frequencies much lower than the 'usual radio frequencies, for example, of the order of 20,000 to 50,000 cycles. Thepercentage frequency variations produced in a carrier wave of the order of magnitude stated lwhen modulated by voice-frequency waves is prob- MULrrrLnX sreNALrNe- SYSTEM.

1919. serial No. 309,715.

ably between .2 of a percent and several percent and is so large that a simple tuned circuit tuned to the carrier frequency is inadequate "to transmit without distortion the range of frequencies represented inl the modulated wave. tionthis distortion is avoided by the use' of a band filter capable of transmitting a range of frequencies with substantially uniform efficiency. This has the property not only of transmitting the desired range of frequencies, but of offering very high attenuation to frequencies outside the desired range. In the drawing, Fig. l shows a schematic circuit diagram of the preferred form of the invention; Fig. 2 shows a modification thereof; and Fig. 3 shows curves relating to the invention.

ilnFig. 3 the solid line is the well-known resonance characteristic of a simple series-` tuned circuit. Assuming that for any frequency to which the given simple tuned circuit is adjusted for resonance, a curve such as the solid line curve applies, then for fre-l quencies 10 percent diHerent from the resonance frequency the transmission falls off from the maximum value m to the value indicated at n. If such a simple circuit is tuned to a carrier frequency of 20,000 cycles and if the carrier wave is modulated by a According to the invencurrent of a frequency of 2000 cycles so as n to comprise frequencies l0 percent less and 10 percent more than the carrier frequency7 the transmission for the eX- treme frequencies will fall to the value n. However, if the same circuit be tuned to 100,000 cycles and this current 'be modulated by a current of 2000 cycles, the transmission is practically uniform for the carrier current and for both extreme frequencies. The dotted curve represents the trans mission properties of a band filter from which it is seen that for a band of frequencies of considerable width the current trans- .mission is practically uniform. A band filter with these characteristics would transmit with negligible distortion a voice modulated carrier wave of base frequency as low as 20,000 cycles, assuming the voice frequencies to lie betwen zero and 2000 cycles.

In Fig. l a high-frequency line l, 2 is shown arranged for two-way repeating with the low frequency lines 3, 4 and 3', 4f, each of which communicates with a corresponding distant station also connected to line l, 2.

Line 1, 2 may be a multiplex carrier wave line', preferably aperiodic, for transmitting simultaneously a plurality of currents of different frequency, and corresponding to eachv carrier frequency or Vchannel thus provided there may be a telephone or other low-frequency line such as 3, 4 or 3\,'4'. Line 3, 4, for instance, may repeat messages into ychannel A, and messages transmitted through' channel A may be received on line 3, 4. In similar manner, the telephone or low-frequency line 3' 4' may cooperate with theB fhannel of the high-frequency line 1, 2.

Tapped off from the line 1, 2 are a number of branches such as 5, 6 and 5', 6'. To" per` mit only the currents comprising channel A to pass into the branch 5, 6 va ilte'r F is provided in the branch, this filter consisting of inductances and capacities, both in series and in shunt of the leads 5, 6, so prop'ofr# tioned as to offer a path of low attenuation to the range of frequencies embraced in the desired modulated carrier wave, but ,to oH'er a high attenuation to other frequencies. The carrier wave with the variations representing the messages traversing channel A, therefore, passes into the branch 5, 6. In the branch 5', 6' there is a filter F', acting f in the manner similar to F .to permit the currents of channel B to flow into the branch 5', 6', but eliminating from this branch currents of other frequencies. In series in the leads 5, 6 are the similar coils 7, 8, 9 and 10, and the leads 5, 6 terminate in a suitable network for balancing the line for the frequencies transmitted through the branch 5, 6. Currents selected from the line 1, 2 by the branch 5, 6 will find a path through coil 11 which is coupled to the input coil 14 ofthe detector 15. By the well-known action of the'detector 15 the currents passing through coil 11 are rendered receivable by the ordinary telephone receiver or other suitable receiver as currents of the same character as were used to modulate the carrier wave of channel A, and in this form they are impressed by means of coils 23 and 24 upon coils 25, 26, 27 and 28, connected in series in the telephone or low-frequency line 3, 4. A net is shown for balancing the line 3, 4 so that the energy thus applied to the line divides equally on each side of the bridging points 29 and 30, without setting up a difference of potential between ypoints 29 and 30. The message represented in the ,modu` lations of the carrier wave of channel A` is thus repeated to the telephone or low-fre` quency line 3, 4 and may be received by the usual telephone receiver at a desired place on said line. A

Signal currents originating on the lowfrequency line 3, 4 will cause differences of potential between bridging points 29 and 30, and therefore across the terminals of the coil 31. This coil is coupled to the input ofthe amplifier which in turn exerts control on the modulator-generator. Any suitable higlrfrequency generator or oscillator may be used, the oscillator 36 shown being a thermionic relay. with a` coupling for feeding a portion of its output energy into the input'circuit, similar to a type shown in U. Patent to Colpitts, Reissue No. 14,380, granted @ctober 23, 1917. By means of the coupling 37 a portion of the output energy is fed back to the input circuit through a tuned circuit so that the oscillationsv are made to persist at a definite frequency. The power output is through the coupling 38 into the circuit including coils 12 and 13 which are arranged with coils 7, 8, 9 and 10 and the line balance in such a way as to impress current variations through the branch 5, 6 on to line 1, 2 without setting up a current iiow through coil 11. By'this provision, the output' energy of the oscillator does not affect 'the detector 15. The waves generated by the oscillator' 36 are modulated in accordance with the signal currents on line 3, 4, conveyed to the modulator-generator through the amplier 33 which has its input coil 32 coupled to coil 31 andits output coil 34 coupled to control winding 35 in the input circuit of the oscillator. The amplifier itself may be of' any suitable type but is shown as the well-known thermionic relay. Line currents from line 3, 4 are impressed through coils 3`1` and 32 on the input circuit of the amplifier 33 and produce similar currents in amplified form in the outputV circuit through the coil 34. These signal currents in their amplified form act upon the control winding 35 to cause corresponding variations in the output waves from generator 36, which pass through the filter F into the line 1, 2. i

The branch 5', 6 is indicated as leading to .a ldector on one side which acts similarly to detector 15 to repeat from high-frequency channel B into the telephone line 3', 4', and on the other side is indicate-d as coupled to the output of a inodulator-generator of B-channel frequency similar to modulatorgenerator 36 by means of which signals on line 3', 4 are repeatedl into the high frequency channel B. An amplifier similar to 33 may be inserted between line 3', 4' and the modulator-generator but has been omitted in the drawing. In similar' manner there may be arranged a two-way repeating means between each high-frequency channel and a corresponding low-frequency line. l

In Fig. 2a contact detector 65,.such as a crystal detector, is shown for use in place of a thermionic type of detector 15, if desired. Certain adjacent elements of the circuit are shown to indicate how the detector .maybe inserted .in the circuit.

While the invention has been described with particular reference to a signaling system it is obvious that it is not limited to signaling but is applicable in general to high-frequency selective systems. While the low frequency modulating currents are referred to as telephone currents it is to be understood that they are not limited to telephone currents. Nor is the invention to be otherwise limited, either by the specific circuit arrangement shown or by the particular details, but only by the scope of the appended claims.

What is claimed is:

l. ln a carrier current system a. high frequency line, a plurality of detectors connected thereto, a balancing network individual to each detector for balancing said line at a given frequency, and an individual band filter connecting each detector to said high frequency line.

2. A high frequency line, a plurality of band filters connected thereto, each for passing a di'erent range of frequencies, and individual balancing networks associated with each of said band filters for balancing said line at the range of frequencies corresponding to that passed by the associated band filter.

3. In a signaling system, a line for carrying a plurality of high-frequency currents each modulated in accordance with signals, a plurality of detectors, a plurality of means for producing modulated high-frequency currents of a plurality of high frequencies for said line, and a plurality of band filters each for transmitting a different modulated high-frequency current in both directions between said line and one of said detectors, and one of said means and said line.

il. lin a multiplex telephone system, a line adapted to transmit high-frequency currents of different frequencies, a plurality of band filters, of respectively different frequency transmission ranges, connected across said line, net circuits each for balancing said transmission line for the range of frequencies transmitted by a different one of said filters, and telephone modulating and detecting means connected between each filter and one of said net circuits.

5. ln a carrier telephone system, a line, means to generate and transmit thereover currents of a plurality of frequencies, including a sustained wave of the order of frequency of 20,000 cycles per second,

means to modulate said wave in accordance with speech and to transmit the resulting modulated wave over said line, means to receive from said line a modulated wave of the order of frequency mentioned and to derive speech currents therefrom, and a band filter for transmitting both of said modulated waves between said line and the transmitting Aand receiving means, and excluding currents of other frequencies from said transmitting and receiving means.

6. ln a signaling system, a transmission line capable of freely transmitting currents of widely differing frequencies, means whereby a plurality of telephone transmissions may be simultaneously effected over said line at a plurality of different frequencies of the order of 20,000 cycles perl second, balancing means for said transmission line comprising separate networks, each simulating the impedance of said transmission line at the frequencies comprisedv in one of said telephone transmissions, and selective means associated with each network for preventing the transmission to said network of other signaling frequencies, said selective means transmitting with practically uniformly negligible attenuation currents of the range of frequencies corresponding to one of said telephone transmissions while attenuating and approximately extinguishing currents outside of said frequency range.

7. ln a multiplex telephone system, a line adapted for carrying a plurality of high-frequency currents, means for producing currents of a plurality of high frequencies for transmission over said line and mea-ns to modulate each high-frequency current in accordance with a separate speech message, a plurality of detectors for deriving speech from received modulated highfrequency currents, and a. plurality of band filters each for selectively passing modulated high-frequency current employed in the transmission of a different conversation, each of said filters serving to transmit modulated high frequency current between said line Aand one of said detectors, and between the modulating means and said line.

In witness whereof, I hereunto subscribe my name this 2nd day of July A. D., 1919.

EDWIN H. COLPITTS. 

